This section provides background information related to the present disclosure which is not necessarily prior art.
A gas-fired, warm air furnace that operates at two or more gas flow rates is generally referred to as a variable or multistage furnace. Multistage furnaces are frequently selected by homeowners for replacement of existing furnaces because they offer increased performance and comfort. But in multistage or variable heating furnaces, the furnace control is only configured for one-way communication with a gas valve. This typically is in the form of a signal applying a voltage source or a variable current signal to the gas valve. Such signals, however, are not capable of providing feedback, and may not be compatible with replacement or retrofit gas valves or other components of the furnace. Accordingly, the inventors hereof have recognized that a need still exists for an improved control of variable stage heating systems.